Oriented perovskite crystals and methods of making the same

ABSTRACT

An aspect of the present disclosure is a method that includes combining a first organic salt (A1X1), a first metal salt (M1(X2)2), a second organic salt (A2X3), a second metal salt (M2Cl2), and a solvent to form a primary solution, where A1X1 and M1(X2)2 are present in the primary solution at a first ratio between about 0.5 to 1.0 and about 1.5 to 1.0, and A2X3 to M2Cl2 are present in the primary solution at a second ratio between about 2.0 to 1.0 and about 4.0 to 1.0. In some embodiments of the present disclosure, at least one of A1 or A2 may include at least one of an alkyl ammonium, an alkyl diamine, cesium, and/or rubidium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/408,383 filed Oct. 14, 2016, the contents of which is incorporatedherein by reference in its entirety.

CONTRACTUAL ORIGIN

The United States Government has rights in this disclosure underContract No. DE-AC36-08GO028308 between the United States Department ofEnergy and the Alliance for Sustainable Energy, LLC, the Manager andOperator of the National Renewable Energy Laboratory.

BACKGROUND

The recent performance improvements in organic-inorganic perovskitesolar cells (PSCs) was brought by incorporating formamidinium (FA⁺)cation into their crystal structure. However, their imbalancedcharge-transport characteristics and inferior light-absorptioncapability, with respect to methylammonium lead halide perovskite(MAPbX₃, X=I, Br, and Cl), have hindered broad application of FA-basedperovskites in optoelectronic applications with a planar architecture.Thus, there remains a need for perovskite films and devices havingimproved physical property and/or performance metrics, as well as a needfor improved methods for manufacturing such films and devices.

SUMMARY

An aspect of the present disclosure is a method that includes combininga first organic salt (A¹X¹), a first metal salt (M¹(X²)₂), a secondorganic salt (A²X³), a second metal salt (M²Cl₂), and a solvent to forma primary solution, where A¹X¹ and M¹(X²)₂ are present in the primarysolution at a first ratio between about 0.5 to 1.0 and about 1.5 to 1.0,and A²X³ to M²Cl₂ are present in the primary solution at a second ratiobetween about 2.0 to 1.0 and about 4.0 to 1.0. In some embodiments ofthe present disclosure, at least one of A¹ or A² may include at leastone of an alkyl ammonium, an alkyl diamine, cesium, and/or rubidium.

In some embodiments of the present disclosure, at least one of A¹ or A²may include at least one of methylammonium, ethylammonium,propylammonium, and/or butylammonium. In some embodiments of the presentdisclosure, at least one of A¹ or A² may include formamidinium. In someembodiments of the present disclosure, at least one of M¹ or M² mayinclude a metal having a 2+ valence state. In some embodiments of thepresent disclosure, at least one of M¹ or M² may include at least one oflead, tin, and/or germanium. In some embodiments of the presentdisclosure, at least one of X¹, X², or X³ may include a halogen. In someembodiments of the present disclosure, at least one of X¹, X², or X³ mayinclude at least one of fluorine, bromine, iodine, and/or astatine. Insome embodiments of the present disclosure, the solvent may include anorganic solvent. In some embodiments of the present disclosure, A¹X¹ andM¹(X²)₂ may form a first reactant pair, A²X³ to M²Cl₂ form a secondreactant pair, and the first reactant pair and the second reactant pairmay be present in the primary solution at a third ratio between about1.0 to 1.0 and about 1.5 to 1.

In some embodiments of the present disclosure, the method may furtherinclude depositing at least a portion of the primary solution onto asolid surface, where the depositing may form a liquid layer thatincludes the primary solution on the solid surface. In some embodimentsof the present disclosure, the depositing may be performed using atleast one of spin coating, blade coating, curtain coating, and/or dipcoating. In some embodiments of the present disclosure, the method mayfurther include, after the depositing, treating at least the liquidlayer, where the treating may convert at least a portion of the liquidlayer to a solid layer that includes a plurality of organic-inorganicperovskite crystals, and the solid layer may be adhered to the solidsurface. In some embodiments of the present disclosure, the plurality oforganic-inorganic perovskite crystals may include A¹ _((1-x-y))A²_(x)A^(3y)M¹ _(z)M² _(1-z)X¹ _(a)X² _(b)X³ _(c)Cl_(d), where x, y, and zmay each be between zero and one inclusively, and a+b+c+d=3.0.

An aspect of the present disclosure is a device that includes aperovskite layer that includes an organic-inorganic perovskite crystal,where the perovskite layer is positioned substantially parallel with aplane, the organic-inorganic perovskite crystal has a molar compositiondefined by A¹ _((1-x-y))A² _(x)A^(3y)M¹ _(z)M² _(1-z)Cl_(d), where x, y,and z are each between zero and one inclusively, and d=3.0, at least oneof A¹, A², and/or A³ includes at least one of an alkyl ammonium, analkyl diamine, cesium, and/or rubidium, and at least one of M¹ or M²includes a metal having a 2+ valence state. In some embodiments of thepresent disclosure, the alky ammonium may include at least one ofmethylammonium, ethylammonium, propylammonium, and/or butylammonium. Insome embodiments of the present disclosure, the alkyl diamine mayinclude formamidinium. In some embodiments of the present disclosure,the metal may include at least one of lead, tin, and/or germanium.

In some embodiments of the present disclosure, the organic-inorganicperovskite crystal may further include X¹ _(a)X² _(b)X³ _(c), wherea+b+c+d=3.0, and at least one of X¹, X², and/or X³ includes a halogen.In some embodiments of the present disclosure, the organic-inorganicperovskite crystal may have a length dimension and a width dimension,and the length dimension and the width dimension may define an aspectratio of the length dimension to the width dimension between about 1.5and about 50. In some embodiments of the present disclosure, the lengthdimension may be oriented substantially perpendicular to the plane. Insome embodiments of the present disclosure, the length dimension may bebetween about 100 nm and about 3000 nm. In some embodiments of thepresent disclosure, the organic-inorganic perovskite crystal may form agrain having a width between about 2 μm and about 5 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures of thedrawings. It is intended that the embodiments and figures disclosedherein are to be considered illustrative rather than limiting.

FIG. 1 illustrates an organic-inorganic perovskite crystal, according tosome embodiments of the present disclosure.

FIG. 2 illustrates a topotactic-oriented attachment (TOA) method forproducing organic-inorganic perovskite crystals substantially orientedalong the (−111) direction, according to some embodiments of the presentdisclosure.

FIG. 3 illustrates a device that incorporates a film oforganic-inorganic perovskite crystals substantially oriented along the(−111) direction, according to some embodiments of the presentdisclosure.

FIGS. 4A through 4D illustrate the crystal structure and morphologicalproperty of a (−111) uniaxial-oriented organic-inorganic perovskite thinfilm, according to some embodiments of the present disclosure. FIG. 4Aillustrates the XRD pattern of the (−111) uniaxial-orientedFA_(0.6)MA_(0.4)PbI_((3-y))Cl_(y) perovskite deposited on (100)-Siwafer. FIG. 4B illustrates the 2D-XRD image of a uniaxial-orientedperovskite deposited on F-doped SnO₂ (FTO) substrate. FIG. 4Cillustrates the tilted-scanning electron microscope (SEM) image of atypical uniaxial-oriented perovskite film. FIG. 4D illustrates aschematic of the uniaxial-oriented organic-inorganic perovskite layer330 constructed from a plurality of organic-inorganic perovskitecrystals (only one referenced 100) deposited on first charge-transportlayer 320 made of c-TiO₂/FTO, further deposited on a substrate 310. Theinset image is a crystal structure image of [−111]-orientedFA_(0.6)MA_(0.4)PbI_((3-y))Cl_(y) perovskite.

FIGS. 5A through 5D illustrate pole figures of a (−111)uniaxial-oriented organic-inorganic perovskite thin film, according tosome embodiments of the present disclosure. (FIG. 5A) (−111) planemeasured at 14.00, (FIG. 5B) (−120) plane measured at 19.8°, (FIG. 5C)(021) plane measured at 24.30, and (FIG. 5D) (−222) plane measured at28.20 of uniaxial-oriented perovskite. The 2theta values of (−120) and(021) planes in the perovskite film were determined from the XRDpatterns of randomly oriented FA_(0.6)MA_(0.4)PbI₃ perovskite preparedusing a conventional solvent-engineering process.

FIG. 6 illustrates the cross-sectional crystal structure of a (−111)uniaxial-oriented organic-inorganic perovskite thin film, according tosome embodiments of the present disclosure. (Panel A) Low-magnificationimage of cross-sectional transmission electron microscopy (TEM) imageand high-resolution TEM (HRTEM) images of (Panel B) top and (Panel C)bottom regions of Panel A. The inset images of each HRTEM image are thefast Fourier-transform (FFT) images. (Panel D) The selected-areaelectrical diffraction (SAED) pattern obtained by 260-nm aperturecorresponding with the marked area in FIG. 6 Panel A using the circle.

FIG. 7 illustrates complete 2D-XRD patterns of theFA_(x)MA_((1-x))PbI_((3-y))Cl_(y) TOA-produced organic-inorganicperovskite crystals with x=0 to 1 formed on FTO substrates fordetermining DCO_({−111}), according to some embodiments of the presentdisclosure. The MAPbI_((3-x))Cl_(x) (x=0) and FAPbI₃ (x=1) perovskiteswere annealed at 100° C. and 150° C. for 50 and 10 min, respectively.Other FA_(x)MA_((1-x))PbI_((3-y))Cl_(y) perovskite were prepared using atwo-step annealing process at 50° C. and 130° C. For comparison, theFA_(0.6)MA_(0.4)PbI₃ perovskite films were also prepared via aconventional solvent-engineering (SE) process. All images are drawn withlog scales.

FIGS. 8A through 8G illustrate crystallographic orientation and growthmechanism information for TOA-produced organic-inorganic perovskitecrystals, according to some embodiments of the present disclosure. FIG.8A illustrate the relative {−111}-oriented crystallinity ofFA_(x)MA_((1-x))PbI_((3-y))Cl_(y) perovskite film as a function of(FAI-PbI₂) molar ratio, where “FA” refers formamidinium. Squaresindicates the randomly oriented FA_(0.6)MA_(0.4)PbI₃ perovskite filmprepared by conventional solvent engineering; diamonds represents pureMALI_((3-x))Cl_(x) and FAPbI₃ perovskites. Inset images illustrate 2-DXRD patterns for determining degree of {−111}-oriented crystallinity.FIG. 8B illustrates the annealing temperature dependence of texturecoefficients of {−111} planes using different precursors:0.6FAI-2.4MAI-PbCl₂ (black squares); 0.6FAI-0.4MAI-PbI₂ (diamonds); and0.6(FAI-PbI₂)-0.4(3MAI-PbCl₂) (circles), wherein “MA” refers tomethylammonium. FIGS. 8C-8G illustrate SEM images and schematics of thetopotactic-oriented attachment (TOA) process. Samples were annealed at130° C. for (FIG. 8C) 10 seconds (FIG. 8D) 30 seconds (FIG. 8F) 180seconds, and (FIG. 8G) 300 seconds.

FIG. 8E illustrates a schematic of a detailed TOA process at theinterface between perovskite and intermediate phase.

FIG. 9 illustrates the morphological evolution of theFA_(x)MA_((1-x))PbI_((3-y))Cl_(y) (0≤x≤1) perovskite used fordetermining DCO{−111}, according to some embodiments of the presentdisclosure.

FIGS. 10A, 10B, and 10C illustrate XRD spectra for organic-inorganicperovskite crystals prepared using different precursors with differentannealing temperature from 100° C. to 150° C., according to someembodiments of the present disclosure. The left sides of FIGS. 10A-10Cillustrate the conventional 2theta scan XRD spectra of perovskite filmsusing 0.6(FAI-PbI₂)-0.4(3MAI-PbCl₂), 0.6FAI-2.4MAI-PbCl₂, and0.6FAI-0.4MAI-PbI₂ precursors, respectively, with various thermalannealing temperatures. The right sides of FIGS. 10A-10C illustratemagnified XRD spectra from 17° to 260 2theta ranges corresponding todashed boxes shown in the left sides of FIGS. 10A-10C, respectively.

FIG. 11 illustrates the representative morphological evolution oforganic-inorganic perovskite crystals prepared via0.6(FAI-PbI₂)-0.4(3MAI-PbCl₂) precursor solution with various annealingtemperature, according to some embodiments of the present disclosure;(Panel A) 100, (Panel B) 110, (Panel C) 130, and (Panel D) 150° C. Asthe TC_({−111}) increases, the perovskite grain size becomes larger andsurface roughness becomes smoother. Maintaining uniform morphologiesunder high annealing temperature can be described by the highmorphological stability of (FAI-PbI₂) parts in0.6(FAI-PbI₂)-0.4(3MAI-PbCl₂) precursor similar that the morphologicalstability of 0.6FAI-0.4MAI-PbI₂ precursor-based perovskite films asshown FIG. 12.

FIG. 12 illustrates the morphologies of organic-inorganic perovskitecrystals deposited using (Panel A)-(Panel C) 0.6FAI-2.4MAI-PbCl₂ and(Panel D)-(Panel F) 0.6FAI-0.4MAI-PbI₂ precursors with 100° C., 130° C.,and 150° C. annealing, respectively, according to some embodiments ofthe present disclosure. The 0.6FAI-2.4MAI-PbCl₂-based perovskites showobvious morphology change from a smooth surface with small pinholes at alower annealing temperature (100° C.) to the ones with wide voidsbetween large island-like grains at higher annealing temperature. Incontrast, the films based on the latter precursors show consistentdendritic morphologies regardless of the annealing temperature.

FIG. 13 illustrates XRD patterns of solid-state-precursor films (SSPs)of (Panel A) 0.6(FAI-PbI₂)-0.4(3MAI-PbCl₂), (Panel B)0.6FAI-2.4MAI-PbCl₂, and (Panel C) 0.6FAI-0.4MAI-PbI₂ precursorformulations, according to some embodiments of the present disclosure.The SSPs are obtained through 50° C. thermal annealing after thespin-coating process. #: chlorine-contained intermediate phase,{circumflex over ( )}: perovskite phase, =: PbI₂, *: FTO, and o: unknownphase.

FIG. 14 illustrates XRD patterns of 0.6(FAI-PbI₂)-0.4(3MAI-PbCl₂)-basedsolid-state precursor films (SSPs) at early stage (10-300 s) of the 130°C., according to some embodiments of the present disclosure. All filmswere quenched through a cool aluminum plate, after appropriateannealing. #: chlorine-contained intermediate phase, {circumflex over( )}: perovskite phase, =: PbI₂, and *: FTO.

FIG. 15 illustrates charge-carrier dynamics and trap density of TOA- andSE-perovskite films where SE refers to organic-inorganic perovskitecrystals prepared using conventional solvent engineering routes). (PanelA) ΦΣ_(μ(t-0)) as a function of absorbed photon fluence (I₀F_(A)) forTOA-perovskite (circle) and for SE-perovskite (square) probed by fp-TRMCwith excitation at 600 nm. The error bar denotes the standard deviation.(Panel B) Representative time-resolved ΦΣμ transients for (top data set)TOA- and (lower data set) SE-perovskites at relatively low excitationintensity (about 7-8×10⁹ photons cm⁻² pulse⁻¹). Solid lines are fittingresults as detailed in text. (Panel C) Dark current-voltage curves ofthe TOA- and SE-perovskites for SCLC analysis. The inset shows thedevice architecture. Two regions are identified based on the exponentvalue of n in IθV^(n): n=1 denotes the ohmic region (solid line); n>3represents the trap-filled region (dashed line).

FIG. 16 illustrates optical absorptance of TOA- and SE-perovskite filmsdeposited on quartz substrate for fp-TRMC measurements, where T is thetransmission and R is the reflectance, according to some embodiments ofthe present disclosure.

FIG. 17 illustrates additional TRMC transient results, according to someembodiments of the present disclosure. (Panel A) A contour plot offrequency-dependent reflected microwave power transients (−ΔP(t)/P) forTOA-perovskite, following excitation at 600 nm. (Panel B) The peakintensities of photoconductance transient signals, ΔG_((t=0)), evincingthe linearity of peak transient signals of (circles) TOA- and (squares)SE-perovskite below the incident excitation photon fluence 0.5×10¹²photons cm⁻²

FIG. 18 illustrates energy-dispersive X-ray spectroscopy (EDS) spectraof TOA- and SE-perovskite, according to some embodiments of the presentdisclosure. (Panel A) EDS spectrum of TOA-perovskite(FA_(0.6)MA_(0.4)PbI_((3-y))Cl_(y)), and (Panel B) SE-perovskite(FA_(0.6)MA_(0.4)PbI₃).

FIG. 19 illustrates cross-sectional SEM images of TOA- and SE-perovskitesolar cells, according to some embodiments of the present disclosure.The thickness of the organic-inorganic perovskite absorbing layers areboth about 450 nm.

FIGS. 20A through 20D illustrate a comparison of PV properties of TOA-and SE-PSCs, according to some embodiments of the present disclosure.FIG. 20A illustrates J-V curves of the TOA- and SE-PSCs with 50-ms scandelay time under AM 1.5G illumination using 0.12-cm² black metalaperture. FIG. 20B illustrates EQE spectra and integrated J_(sc). FIG.20C illustrates stabilized photocurrent density and PCE of TOA- andSE-PSCs biased at 0.83 V and 0.93 V, respectively. FIG. 20D illustratesscan rate (delay time) dependence of forward- and reverse-scan PCEs forTOA- and SE-PSCs. PCEs were normalized to that obtained from reversescan with 50-ms delay time.

FIG. 21 illustrates histograms of PCEs of the SE- andTOA-perovskite-based PHJ solar cells, according to some embodiments ofthe present disclosure. For statistics, 23 and 22 devices are tested,respectively. The histograms filled with oblique lines are obtained fromforward-scan PCEs, and histograms filled with solid color are obtainedfrom reverse-scan PCEs.

FIGS. 22A and 22B illustrate a comparison between certified stabilizedPCE output and PCE obtained from general J-V curve, according to someembodiments of the present disclosure. FIG. 22A illustrates independentcertification of typical uniaxial-oriented perovskite PHJ device fromNational Renewable Energy Laboratory (NREL) via asymptoticalstabilization method, confirming a PCE of 17.17%. FIG. 22B illustratesthe J-V curve of the same device measure at AM 1.5G illumination in ourlab and forward- and reverse-scan PCEs. The certificated, stabilized PCEshowed 96% of reverse-scan PCE.

FIGS. 23A and 23B illustrate crystal structure and morphology ofuniaxial-oriented perovskites prepared by TOA process with variouscompositions, according to some embodiments of the present disclosure.FIG. 23A illustrates XRD patterns and FIG. 23B morphologies ofMAPbI_((3-y))Cl_(y), (FA_(0.5)MA_(0.2))PbI_((3-y))Cl_(y) and(Cs_(0.05)FA_(0.55)MA_(0.4))Pb(I_((2.9-y))Br_(0.1)Cl_(y)) prepared byTOA process. The indexing labels mean the following: {circumflex over( )}=perovskite phase, and *=FTO.

REFERENCE NUMBERS

-   -   100 . . . organic-inorganic perovskite crystal    -   110 . . . first cation    -   120 . . . second cation    -   130 . . . anion    -   200 . . . method    -   210 . . . preparing a first solution    -   220 . . . preparing a second solution    -   230 . . . mixing    -   240 . . . depositing    -   250 . . . treating    -   300 . . . device    -   310 . . . substrate    -   320 . . . first charge-transport layer    -   330 . . . organic-inorganic perovskite layer    -   340 . . . second charge-transport layer    -   350 . . . additional layer DETAILED DESCRIPTION

The present disclosure may address one or more of the problems anddeficiencies of the prior art discussed above. However, it iscontemplated that some embodiments as disclosed herein may prove usefulin addressing other problems and deficiencies in a number of technicalareas. Therefore, the embodiments described herein should notnecessarily be construed as limited to addressing any of the particularproblems or deficiencies discussed herein.

The present disclosure relates to methods that enable the production oforganic-inorganic perovskite crystals. As described herein, such methodsare referred to as topotactic-oriented attachment (TOA) processes ormethods, which are shown to enable the growth of at leastformamidinium-based (FA-based) organic-inorganic perovskite films,having physical properties that include (−111) uniaxial orientation,micron-grain morphology, high crystallinity, and low trap density (about4×10¹⁴ cm⁻³). Organic-inorganic perovskites synthesized using these TOAmethods are shown to possess unprecedented 9-GHz charge-carrier mobility(about 70.8 cm²/V·s) via time-resolved microwave conductivityexperiments-more than double what has been reported for variousorganic-inorganic polycrystalline perovskites-almost 300% higher thanrandomly oriented perovskite thin films made by other synthesis methods.In addition, planar perovskite solar cells (PSCs) usingorganic-inorganic perovskite films made by the TOA methods describedherein are shown to have a power-conversion efficiencies (PCE); e.g. upto about 19.7% (stabilized PCE of 19.0%). The present disclosuredemonstrates the versatility of the disclosed TOA processes for growingvarious organic-inorganic perovskite compositions, includingtriple-cation and mixed-halide organic-inorganic perovskite crystals andfilms. Some examples of organic-inorganic perovskite films produced bythe TOA processing methods described herein includeFA_(0.6)MA_(0.4)PbI_((3-y))Cl_(y), MAPbI_((3-y))Cl_(y),FA_(0.5)MA_(0.2)PbI_((3-y))Cl_(y), where 0≤y≤3.0, andFA_(0.55)MA_(0.4)Cs_(0.05)PbI_((2.9-y))Br_(0.1)Cl_(y), where 0≤y≤2.9.

Thus, the present disclosure relates generally to methods of makingorganic-inorganic perovskite crystals. In addition, the presentdisclosure relates to unique organic-inorganic perovskite crystalshaving unique physical property and performances metrics, as well asfilms and devices (e.g. solar cells) that incorporate the uniqueorganic-inorganic perovskite crystals. FIG. 1 illustrates thatorganic-inorganic perovskite crystals 100 (as well as inorganicperovskite crystals) may organize into cubic/pseudocubic crystallinestructures and may be described by the general formula AMX₃, where X isan anion 130 and A and M are first cations 110 and second cations 120,respectively, typically of different sizes (A typically larger than M).In a cubic unit cell, the second cation 120 resides at the eight cornersof a cube, while the first cation 110 is located at the center of thecube and is surrounded by six anions 130 (located at the face centers)in an octahedral [MX₆]⁴⁻ cluster (unit structure). Typical inorganicperovskites include cesium halide perovskites such as CsPbI₃ andCsPbBr₃, and titanium oxide (calcium titanate) minerals such as, forexample, CaTiO₃ and SrTiO₃. In some structures, the first cation 110 mayinclude a nitrogen-containing organic compound such as an alkyl ammoniumcompound. The second cation 120 may include a metal and the anion 130may include a halogen.

Additional examples of a first cation 110 include organic cations and/orinorganic cations. First cations 110 may be an alkyl ammonium cation,for example a C₁₋₂₀ alkyl ammonium cation, a C₁₋₆ alkyl ammonium cation,a C₂₋₆ alkyl ammonium cation, a C₁₋₅ alkyl ammonium cation, a C₁₋₄ alkylammonium cation, a C₁₋₃ alkyl ammonium cation, a C₁₋₂ alkyl ammoniumcation, and/or a C₁ alkyl ammonium cation. Further examples of firstcations 110 include methylammonium (CH₃NH³⁺), ethylammonium (CH₃CH₂NH³),propylammonium (CH₃CH₂ CH₂NH³⁺), butylammonium (CH₃CH₂ CH₂ CH₂NH³⁺),formamidinium (NH₂CH═NH²⁺), and/or any other suitablenitrogen-containing organic compound. In other examples, a first cation110 may include an alkylamine. Thus, a first cation may include anorganic component with one or more amine groups, resulting in theformation of an organic-inorganic perovskite crystal 100. For example, afirst cation 110 may be an alkyl diamine such as formamidinium(CH(NH₂)₂).

Examples of metallic second cations 120 include, for example, lead, tin,germanium, and or any other 2+ valence state metal that maycharge-balance the organic-inorganic perovskite crystal 100. Examplesfor an anion 130 include halogens: e.g. fluorine, chlorine, bromine,iodine and/or astatine. In some cases, an organic-inorganic perovskitecrystal 100 may include more than one anion 130, for examplecompositions having different halogens; chlorine and iodine, bromine andiodine, and/or any other suitable pairs of halogens. In other cases, anorganic-inorganic perovskite crystal 100 may include two or morehalogens of fluorine, chlorine, bromine, iodine, and/or astatine.

Thus, a first cation 110, a second cation 120, and an anion 130 may beselected within the general formula of AMX₃ to produce a wide variety oforganic-inorganic perovskite crystals 100, including, for example,methylammonium lead triiodide (CH₃NH₃PbI₃), and mixed organic-inorganicperovskites such as CH₃NH₃PbI_(3-x)Cl_(x) and CH₃NH₃PbI_(3-x)Br_(x). So,an organic-inorganic perovskite crystal 100 may have more than onehalogen element, where the various halogen elements are present in noneinteger quantities; e.g. where x varies from 0 to 3 in more than justinteger values; e.g. 1, 2, or 3. In addition, perovskite halides, likeother organic-inorganic perovskites, can form three-dimensional (3-D),two-dimensional (2-D), one-dimensional (1-D) or zero-dimensional (0-D)networks, possessing the same unit structure.

As stated above, the first cation 110 may include an organic constituentin combination with a nitrogen constituent. In some cases, the organicconstituent may be an alkyl group such as straight-chain or branchedsaturated hydrocarbon group having from 1 to 20 carbon atoms. In someembodiments, an alkyl group may have from 1 to 6 carbon atoms. Examplesof alkyl groups include methyl (C₁), ethyl (C₂), n-propyl (C₃),isopropyl (C₃), n-butyl (C₄), tert-butyl (C₄), sec-butyl (C₄), iso-butyl(C₄), n-pentyl (C₅), 3-pentanyl (C₅), amyl (C₅), neopentyl (C₅),3-methyl-2-butanyl (C₅), tertiary amyl (C₅), and n-hexyl (C₆).Additional examples of alkyl groups include n-heptyl (C₇), n-octyl (C₅)and the like. The methods provided herein, describe methods forproducing organic-inorganic perovskites having compositions andcomponents as described above, where the resultant organic-inorganicperovskites include a plurality of crystals that are all significantlyoriented in when direction (e.g. across the width of anorganic-inorganic perovskite film).

FIG. 2 summarizes a TOA method 200 for synthesizing organic-inorganicperovskite materials (e.g. crystals, films, and/or devices), accordingto some embodiments of the present disclosure. In particular, the method200 summarizes an example of a TOA method for producingorganic-inorganic perovskite crystals that are significantly orientedrelative to a single axis direction, with detailed examples of both TOAmethods and the resultant organic-inorganic perovskite materialsprovided below. Thus, in the example of FIG. 2, the TOA method 200begins with the preparing 210 of a first solution (solution not shown).The first solution may include a first organic salt (A¹X¹) and a firstmetal salt (M¹(X²)₂) in a first solvent such that the first organic salt(not shown in FIG. 2) and the first metal salt (not shown) may bepresent at a first ratio between about 0.5 to 1.0 and about 1.5 to 1.0.As used herein, the term “about” refers to statistical variation at theendpoints of a given range. So, to provide a numerical definition forthe term “about”, the term “about” refers to a statistical variationthat does not exceed 5% of the absolute value of an endpoint value.

In some embodiments of the present disclosure, the preparing 210 of thefirst solution may produce a first solution where the first organic saltand the first metal salt may be present at a first ratio of about one toone. The method 200 may continue with the preparing 220 of a secondsolution (not shown in FIG. 2). A second solution may include a secondorganic salt (A²X³) and a second metal salt (M²Cl₂) in a second solventsuch that the second organic salt (not shown in FIG. 2) and the secondmetal salt (not shown) may be present at a second ratio between about2.0 to 1.0 and about 4.0 to 1.0. In some embodiments of the presentdisclosure, the preparing 220 of the second solution may produce asecond solution where the second organic salt and the second metal saltmay be present at a second ratio of about three to one. The TOA method200 may then continue with the mixing 230 of the first solution and thesecond solution to produce a third solution (not shown in FIG. 2) havinga third ratio of the first solution to the second solution between about0.5 to 1.0 and about 2.0 to 1.0. In some embodiments of the presentdisclosure, the mixing 230 of the first solution with the secondsolution to produce a third solution may be at a third ratio of about1.5 to 1.0. In so doing, the third solution, the final target solutionto be utilized in the subsequent method steps, may have a final ratio of(A¹X¹):(M¹(X²)₂) to (A²X³): (M²Cl₂) between about 0.5 to 1.0 and about2.0 to 1.0. In some embodiments of the present disclosure, the third(final target) solution may have a final ratio of (A¹X¹):(M¹(X²)₂) to(A²X³): (M²Cl₂) of about 1.5 to 1.0.

Although, the example of FIG. 2 illustrates a TOA method 200 thatprepares two separate solutions (a first solution and a secondsolution), followed by the mixing of the two separate solutions toproduce a third solution, it should be understood that the thirdsolution, the final target solution, may also be produced in a singlestep. In such an example, one or more solvents may be utilized in asingle, final target solution with the first organic salt, the secondorganic salt, the first metal salt, and the second metal salt such thatthe first organic salt and the first metal salt are present at ratiobetween about 0.5 to 1.0 and about 1.5 to 1.0. In addition, the secondorganic salt and the second metal salt may be included in the finaltarget solution such that the second organic salt and the second metalsalt may be present at a ratio between about 2.0 to 1.0 and about 4.0 to1.0. As a result, the final target solution may have a final ratio of(A¹X¹):(M¹(X²)₂) to (A²X³): (M²Cl₂) between about 2.0 to 1.0 and about0.5 to 1.0. In some embodiments of the present disclosure, the finaltarget solution may have a final ratio of (A¹X¹):(M¹(X²)₂) to (A²X³):(M²Cl₂) of about 1.5 to 1.0. As used herein, unless specified otherwise,all ratios are on a molar basis.

In some embodiments of the present disclosure, A¹ and/or A² may includeat least one of methylammonium (MA), formamidinium (FA),diethylammonium, dimethylammonium, ethane 1,2-diammonium, ethylammonium,methylammonium, iso-butylammonium, n-butylammonium, t-butylammonium,iso-propylammonium, n-propylammonium, propane 1,3-diammonium,n-octylammonium, phenylethylammonium, polyethylenimine, cesium, and/orrubidium. Thus, A₁ and/or A₂ may include at least one of the firstcations 110 described above and shown in FIG. 1. M¹ and/or M² mayinclude at least one of lead, tin, silver, and/or bismuth. Thus, M¹and/or M² may include at least one of the second cations 120 describedabove and shown in FIG. 1. All of those chemicals may be dissolved in apure or mixed organic solvent based on at least one of dimethylformamide(DMF), dimethylacetamide (DMA), butyrolactone (GBL), dimethyl sulfoxide(DMSO), and/or N-methyl-2-pyrrolidone (NMP). The concentration of anyone of the the components contained in the starting solutions and/or thefinal target solution may be between about 0.1 M and about 2 M.Solutions may be agitated at a temperature between about 25° C. andabout 80° C. for a time period between about 0.5 hours and about 12hours.

Referring again to FIG. 2, the example TOA method 200 illustrated mayproceed with the depositing 240 of the final target solution onto asubstrate (not shown in FIG. 2). The depositing 240 may be accomplishedby a variety of solution processing methods such as at least one of spincoating, blade coating, curtain coating, dip coating, etc. Thedepositing 240 will result in the application of a liquid coating of thefinal target solution deposited onto a surface of the substrate. In someembodiments of the present disclosure, such a coating may have athickness between about 100 nm and 3000 nm.

The TOA method 200 may continue with a treating 250 of the liquidcoating on the substrate, for example the thermal treating of the liquidcoating, resulting in the transformation of the liquid coating to asolid film and/or layer of organic-inorganic perovskite crystals. Insome embodiments of the present disclosure, the treating 250 may becompleted at a temperature of about 120° C. or higher, or between about120° C. and about 200° C. In some embodiments of the present disclosure,the treating 250 may be completed for a time duration of about 5 minutesor longer, or between about 5 minutes and about 60 minutes. The treating250 may be completed in an inert environment, for example in a nitrogengas and/or argon gas environment. In general, the resultantorganic-inorganic perovskite crystals formed may be defined by thecomposition

A¹ _((1-x-y))A² _(x)A³ _(y)M¹ _(z)M² _(1-z)X¹ _(a)X² _(b)X³ _(c)Cl_(d)

where x, y, and z are each between zero and one inclusively, anda+b+c+d=3.0. For example, an organic-inorganic perovskite crystal madeby the TOA methods described herein may includeFA_(0.6)MA_(0.4)PbI_((3-d))Cl_(d) (A¹=FA, A²=MA, y=0, M¹=Pb, X¹=I,b=c=0, x=0.4, and y=0), MAPbI_((3-d))Cl_(d) (A¹=MA, M¹=Pb, X¹=I, b=c=0,x=y=0) and/or FA_(0.5)MA_(0.2)PbI_((3-d))Cl_(d) (A¹=FA, A²=MA, M¹=Pb,X¹=I, b=c=0, x=0.2, and y=0), where d is between zero and three,inclusively, for all three examples. In some embodiments of the presentdisclosure, an organic-inorganic perovskite crystal made by the TOAmethods described herein may includeFA_(0.55)MA_(0.4)Cs_(0.05)PbI_((3.0-0.1-d))Br_(0.1)Cl_(d) (A¹=FA, A²=MA,A³=Cs, M²=Pb, X¹=I, X²=Br, x=0.4, y=0.05, b=0.1, c=0,), where d isbetween zero and about 2.9, inclusively, due to the inclusion of bromidein the example of an organic-inorganic perovskite crystal. For someembodiments of the present disclosure, for TOA processing, a finalprecursor solution may have a final ratio of (A¹X¹):(M¹(X²)₂) to (A²X³):(M²Cl₂) between about 1.0 to 1.0 and about 1.5 to 1.0, respectively.

As described herein, the organic-inorganic perovskite crystals resultingfrom examples of the TOA method described herein have a variety ofunique characteristics, including crystals having an aspect ratio(length dimension divided by width dimension) between about 1.5 and 50,with a length dimension between about 100 nm and about 3000 nm. Further,the organic-inorganic perovskite crystals may be significantly orientedsuch that the length dimension of each individual crystal issubstantially aligned relative to a reference axis and/or plane. Forexample, relative to a planar substrate, the individual crystals may bealigned substantially perpendicular to the substrate. Relative to thethickness dimension of a film constructed of a plurality oforganic-inorganic perovskite crystals, the individual crystals may bealigned substantially parallel with the thickness dimension. Incrystallographic terms, organic-inorganic perovskite crystals producedby embodiments of the TOA methods described herein demonstrate highcrystallinity in the (−111) with uniaxial orientation, with low trapdensities (as low as 4×10¹⁴ cm⁻³), compared with that of previousreported values (about 10¹⁶-10¹⁷ cm⁻³), and grain sizes between about 2μm and about 5 μm.

FIG. 3 illustrates an example of a device 300 that incorporates anorganic-inorganic perovskite layer 330 made from a plurality oforganic-inorganic perovskite crystals (only two of the plurality calledout with reference numbers 100 a and 100 b) produced by embodiments ofthe TOA method described herein. This device 300 includes a substrate310, a first charge transport layer 320 (e.g., TiO₂, SnO₂, and/or ZnOlayer), the organic-inorganic perovskite layer 330, a second chargetransport layer 340 (e.g., spiro-OMeTAD,poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), and/orpoly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)),and an additional layer 350 (e.g. a conducting layer of gold, silver,and/or copper). FIG. 3 illustrates an embodiment where the lengths(versus widths) of the individual organic-inorganic perovskite crystals(100 a and 100 b) are aligned substantially parallel with the y-axisreference axis (e.g. thickness of the substrate), and substantiallyperpendicular to the width dimension (x-axis) and length dimension(z-axis) of the substrate 310.

Referring again to FIG. 3, a substrate 310 such as fluorine-doped tinoxide (FTO), was deposited with a compact TiO₂ layer having a thicknessbetween about 10 nm and about 60 nm as an electron-transport layer. Thislayer was deposited by spray pyrolysis at 450° C. using 0.2 M titaniumdiisopropoxide bis(acetylacetonate) in 1-butanol solution, followed by450° C. annealing for about 1 hour. An organic-inorganic perovskitelayer 330 was deposited in a dry nitrogen box using a spin coatingmethod. In this example, the spin coating was a two-step procedure withthe first step completed at 500 rpm for about 15 seconds, and the secondstep completed at 2000 rpm for about 45 seconds. For the control sample(by solvent engineering (SE))), a precursor solution prepared by atwo-step spin coating procedure at 1,000 rpm and 4,000 rpm for 60seconds and 40 seconds, respectively. At 30 seconds of the secondspin-coating step, 0.7 mL of diethyl ether was drop-casted on thespinning substrate (e.g. solvent engineering (SE)). After the spincoating, the resultant liquid coatings were annealed at about 50° C. forabout 5 minutes in a first thermal treating step, followed sequentially,by a second thermal treating step at 130° C. for about 10 minutes toform the final organic-inorganic perovskite layer 330. After annealing,60 μL of a hole-transport layer (HTL) solution (72 mg of spiro-OMeTAD,29 μL of 4-tert-butylpyridine, 17 μL of Li-TFSI solution (520 mg ofLi-TFSI in 1 mL acetonitrile) and 20 μL of FK102 Co(III) TFSI salt (300mg FK102 Co(III) TFSI in 1 mL acetonitrile) in 1 mL of chlorobenzene)was spin-coated on the perovskite/c-TiO₂/FTO device at 3,500 rpm forabout 30 seconds. Finally, a 130-nm Ag layer was deposited on the HTL bythermal evaporation with 0.15 nm s⁻¹ deposition rate, resulting in thecompleted device.

Structural information of thin films of organic-inorganic perovskitecrystals films was obtained through analysis of their X-ray diffraction(XRD) patterns. In FIG. 4A, the XRD patterns of anFA_(0.6)MA_(0.4)PbI_(3-y)Cl_(y) organic-inorganic perovskite crystallayer deposited on a (100) silicon substrate by a TOA-method onlyexhibited planes of P3m1 trigonal structure, suggesting that theTOA-deposited organic-inorganic perovskite was highly oriented along a[−111] uniaxial direction. Two-dimensional XRD (2D-XRD) profiles shownin FIG. 4B further illustrate the uniaxial-orientation feature throughthe two bright spots at 14.00 and 28.20 (corresponding, respectively, tothe diffractions from the (−111) and (−222) planes). Pole figures of theorganic-inorganic perovskite crystals produced by TOA method (such aperovskite hereinafter also referred to generally as a “TOA-perovskite”)also confirm the uniaxial [−111]-orientation with the strongsingle-spots of (−111) and (−222) planes and clear ring-shape of (−120)and (021) planes (see FIGS. 5A-5D).

FIG. 4C presents the tilted SEM image of an example TOA-perovskitedeposited on c-TiO₂/F-doped SnO₂ (FTO) substrate. FIG. 4C shows that theperovskite layer is fairly smooth and densely packed with about2-5-μm-sized grains. The cross-sectional crystallographic information ofthis example TOA-perovskite was examined using high-resolutiontransmission electron microscopy (HRTEM), as shown in FIG. 6. Noperovskite grain boundaries parallel to the substrate were found (seeFIG. 6 Panel A). Two selected (top and bottom) regions of theorganic-inorganic perovskite crystal film show identical lattice spacingof 3.15 Å from the (−222) planes (see FIG. 6 Panels B and Crespectively). Their fast Fourier-transform (FFT) patterns (see insetsof FIG. 6 Panels B and C respectively) match well with the selected-areadiffraction patterns (see FIG. 6 Panel D; the circled region in FIG. 6Panel A). These crystallographic and morphological results stronglyindicate that TOA-derived organic-inorganic perovskite crystal layer iscomposed substantially of (−111) uniaxial-oriented crystals alignedperpendicular to the substrate, and that other planes such as (−120) and(021) are randomly oriented along in-plane directions, as illustrated inFIG. 4D.

Thin films made of organic-inorganic perovskite crystals were preparedby a solution processing method, e.g. spin-coating a precursor startingsolution containing x(FAI-PbI₂):(1−x)(3MAI-PbCl₂) (0≤x≤1), where FAI wasthe first organic salt, PbI₂ the first metal salt, MAI the secondorganic salt, and PbCl₂ the second metal salt. Further, FAI and PbI₂were mixed at a first ratio of about one to one, and MAI and PbCl₂ weremixed at a second ratio of about three to one. Finally, the (FAI-PbI₂)pair was mixed with the (3MAI-PbCl₂) pair at a ratio that varied from1:0 to 0:1. After spin-coating of the resultant solution on thesubstrate, resulting in a liquid coating of the solution on thesubstrate, the substrate and liquid coating were thermally treated (e.g.annealed) without using any additional solvent removal step. 2D-XRDpatterns of the resultant TOA-perovskite thin films with varying x,where x refers to x(FAI-PbI₂):(1−x)(3MAI-PbCl₂) (0≤x≤1), show a clearcorrelation between organic-inorganic perovskite composition andcrystallographic properties (see FIG. 7). To capture both crystallinityand orientation, the degree of crystallographic orientation (DCO)relative to the {−111} planes was defined, denoted as DCO_({−111})).

Briefly, DCO_({−111}) measures the proportion of the crystallinity ofthe oriented {−111} planes (e.g., (−111) and (−222) planes), and it isdetermined from the integrated intensities of each plane over the entireχ range of 2D-XRD patterns using Equation 2 (see below). FIG. 8A showsthat the DCO_({−111}) values of the TOA-produced organic-inorganicperovskite crystals depend strongly on the fraction x of (FAI-PbI₂)component pairing provided in the starting solution. DCO_({−111}) valuesincreased from a value of about 2.0 for a starting solution targetingFA_(0.4)MA_(0.6)PbI_(3-y)Cl_(y) to a value of about 5.2 for a startingsolution targeting FA_(0.5)MA_(0.5)PbI_(3-y)Cl_(y), and reached themaximum of about 5.7 for a starting solution targetingFA_(0.6)MA_(0.4)PbI_(3-y)Cl_(y); 0≤y≤3.0. In contrast, a perovskite filmprepared by using solvent engineering (referred to hereinafter as a“SE-perovskite”) with the same FA:MA ratio yielded a value forDCO_({−111}) of only 0.5. For the conventional mixed-halideMAPbI_((3-y))Cl_(y) perovskite prepared using the recipe from Lee et al.(Science 338, 643-647 (2012)), the DCO along the preferred orientation[110]-direction is about 0.76. Thus, the high DCO_({−111}) value of theuniaxially oriented FA_(0.6)MA_(0.4)PbI_((3-y))Cl_(y) perovskiteindicates that the new TOA processing method not only enables (−111)uniaxial orientation, but also leads to a high degree of crystallinityof the organic-inorganic perovskite crystal film.

SEM images (see FIG. 9) show that the FA_(x)MA_((1-x))PbI_((3-y))Cl_(y)inorganic-organic perovskite crystal film morphology also depends on the(FAI-PbI₂) ratio x. With an increasing amount of the (FAI-PbI₂) pair inthe precursor solution, the grain size decreased from about 25 μm (atx=0.2) to about 200 nm (at x=0.8) and the void space between grains alsodecreased concomitantly. When x reached between about 0.5 and about 0.6,the resulting organic-inorganic perovskite crystal films were dense andflat with large grains (between about 2 μm and about 5 μm). However,when x was further increased to 0.7 or more, rougher perovskite grainswere formed in conjunction with more random orientation in theorganic-inorganic perovskite crystal film, as reflected by the muchreduced DCO values (See FIG. 8A).

To understand the growth mechanism for forming the uniaxial orientationand dense, smooth, micronized morphology of TOA-processedFA_(0.6)MA_(0.4)PbI_((3-y))Cl_(y) organic-inorganic perovskite crystalfilms, three different perovskite precursor formulations werecompared: 1) 0.6(FAI-PbI₂)-0.4(3MAI-PbCl₂); 2) 0.6FAI-2.4MAI-PbCl₂; and3) 0.6FAI-0.4MAI-PbI₂. Annealing temperatures were also varied for thethree different precursor formulations. Thus, the first formulation useda first reactant pair of a first organic salt of FAI and a first metalsalt of PbI₂, at a first ratio of the first organic salt to the firstmetal salt of about 1:1. The first formulation also used a secondreactant pair of a second organic salt of MAI and a second metal salt ofPbCl₂, at a second ratio of the second organic salt to the second metalsalt of about 3:1. Finally, the first formulation used a third ratio ofthe first reactant pair to the second reactant pair of about 0.6:0.4.The second formulation used a first organic salt of FAI, a secondorganic salt of MAI, a first metal salt of PbCl₂, with each of these ata ratio of FAI:MAI:PbCl₂ of about 0.6:2.4:1.0. The third formulationused a first organic salt of FAI, a second organic salt of MAI, andfirst metal salt of PbI₂, with each of these at a ratio of FAI:MAI:PbI₂of about 0.6:0.4:1.0.

The impact of the three precursors formulations on the resultantorganic-inorganic perovskite crystal orientations can be obtained bydetermining the texture coefficient of {−111} planes, noted asTC_({−111}), which can be calculated from XRD patterns (see FIGS. 10A,10B, and 10C) using Equation 3 (see below). FIG. 8B shows thatTC_({−111}) values for organic-inorganic perovskites derived from the0.6FAI-2.4MAI-PbCl₂ precursor formulation and the 0.6FAI-0.4MAI-PbI₂precursor formulation are about 6 and 2, respectively, with negligibledependence on the annealing temperature. These values representapproximately the upper and lower bounds for completely textured andrandomly oriented films. For perovskites based on the0.6(FAI-PbI₂)-0.4(3MAI-PbCl₂) precursor formulation, the TC_({−111})value increases rapidly with temperature, approaching 6 at 120° C., andstaying unchanged at higher temperature (see FIG. 8B). Interestingly,perovskites using this precursor exhibited uniform and dense morphologyregardless of annealing temperature (see FIG. 11), which contrastssignificantly to perovskites prepared using the other two precursorsformulations (see FIG. 12). The dramatic increase of TC_({−111}) valuesand grain size with higher annealing temperature for organic-inorganicperovskites crystals using 0.6(FAI-PbI₂)-0.4(3MAI-PbCl₂) precursorcannot be simply explained by grain coarsening, halide mixing effects,or topotactic self-assembly nucleation/growth.

Further analysis of morphological (see FIGS. 8C-G) and crystal-structureevolutions (see FIGS. 13 and 14) of 0.6(FAI-PbI₂)-0.4(3MAI-PbCl₂)solid-state-precursor (SSP) film during the early stages of theannealing process (˜300 seconds at 50° C. and between about 10 secondsand about 300 seconds at 130° C.) provides insight on a formationprocess of uniaxial-oriented organic-inorganic perovskite films. The XRDpatterns shown in FIG. 13 clearly show the coexistence ofchlorine-containing intermediates and perovskite phases for the SSP filmbased on the 0.6(FAI-PbI₂)−0.4(3MAI-PbCl₂) precursor formulation, incomparison to the SSP films using the 0.6FAI-2.4MAI-PbCl₂ and0.6FAI-0.4MAI-PbI₂ precursor formulations. When annealed at 130° C. forabout 10 seconds, distinct perovskite and intermediate morphologies (seeFIG. 8C) were observed, which is consistent with the XRD patterns shownif FIG. 14. After about 30 seconds of annealing, several micron-sizedorganic-inorganic perovskite grains appeared at the interface betweenperovskite and intermediates (see FIG. 8D). During this early-stageannealing, the perovskite (−111) and (−222) plane diffractionintensities increased dramatically, whereas the diffraction peaks fromplanes started to disappear (see FIG. 14).

In general, when the agglomeration of nanoparticles coarsens withhigh-energy conditions (e.g., hydrothermal growth), oriented attachmentbetween neighboring particles involving spontaneous self-organizationalong a common crystallographic orientation and sequential coalescencecould occur to reduce the overall energy. As schematically illustratedin FIG. 8E, the aforementioned simultaneous evolution of film morphologyand crystalline orientation of perovskites may be explained by orientedattachment along [−111] direction during the topotactic phasetransformation from intermediates to perovskites. Thus, this new growthmechanism is referred to herein as “topotactic-oriented attachment”. Theresults herein suggest that above about 120° C., TOA growth is dominantover other competing crystal-formation processes (e.g., topotacticself-assembly nucleation/growth or direct perovskite formation). DuringTOA growth, the rearrangement of organic-inorganic perovskite crystaldomains occurs, leading to a single dominant orientation. As annealingand film formation continue, inorganic-organic perovskite grainsgradually coalesce and become larger, while the intermediate surroundingorganic-inorganic perovskite crystals diminish (see FIG. 8F). Finally,after about 300 seconds of annealing, the organic-inorganic perovskitefilm becomes densely packed with a smooth surface (see FIG. 8G) and theintermediate phase completely disappears (see FIG. 14).

The impact of TOA-perovskite growth on charge transport in the resultantorgani-inorganic perovskite crystals was studied by comparing thephotoconductance (ΔG) of TOA- and SE-perovskite films usingflash-photolysis time-resolved microwave conductivity (fp-TRMC). Infp-TRMC, ΔG(t) is related to the product (ΦΣμ(t)) of carrier-generationyield (Φ(t)) and both electron (μ_(e)) and hole (μ_(h)) mobilities(Σμ=μ_(e)+μ_(h)) (20). In this work, c(t) values for theseorganic-inorganic perovskite crystals are near unity as determined frominternal quantum efficiencies of TOA- and SE-PSCs (94% and 96%,respectively) at the excitation wavelength (600 nm). FIG. 15 Panel Adisplays ΦΣμ_((t=0)) for TOA- and SE-perovskites as a function ofabsorbed photon fluence (I₀F_(A)), where I₀ is the excitation fluenceand FA is the film absorptance (see FIG. 16). The representative ΦΣμ(t)transient signal decays for both TOA- and SE-perovskite films are shownin FIG. 15 Panel B. At the low range of excitation fluences (<6×10¹¹photons cm⁻²), many-body interactions (e.g., carrier-carrierannihilation or carrier quenching) appear to be negligible, and theimaginary contribution of photoconductivity is also negligible (see FIG.17, Panels A and B). With the near-unity Φ, the maximum Σμ_((t=0)) ofTOA-perovskites is as high as 70.8 cm²V⁻¹ s⁻¹, which is ˜2.8 timeshigher than that of SE-perovskite (maximum Σμ_((t=0))=25.0 cm²V⁻¹ s⁻¹).

The 25.0 cm²V⁻¹ s⁻¹ of Σμ_((SE)) value for SE-perovskite was comparableto those previously reported 9-GHz Σμ values (1-30 cm²V⁻¹ s⁻¹) forvarious perovskite samples. Thus, this 70.8 cm²V⁻¹ s⁻¹ of Σμ_((TOA)) hasexceeded all previously reported 9-GHz Σμ values for organic-inorganicpolycrystalline perovskite thin films, unambiguously supporting theenhanced electrical properties of organic-inorganic perovskite crystalsformed by the TOA methods described herein. In general, charge-carriermobilities can be affected by various factors such as grain size,compositional doping, and crystal orientation, film architectures (e.g.,planar or mesoscopic), and perovskite compositions (e.g., mixedhalides). Thus, in the work described herein, the grain sizes of bothTOA- and SE-perovskites are too large (>400 nm) to affect fp-TRMCcarrier mobilities. Given the same composition and film architecture,for both TOA- and SE-perovskites, the unprecedented Σμ in TOA-perovskitemay be ascribed mainly to uniaxial TOA-perovskite growth with theenhanced crystallinity and low defect (or trap) density. FIG. 15 Panel Cshows the space-charge-limited current (SCLC) analysis of the TOA- andSE-perovskite samples. The trap density, n_(t), is linearly proportionalto the onset voltage (V_(TFL); see Equation 3 below) at the kink pointof the current-voltage (I-V) response, which represents a transitionfrom the linear ohmic region (I∝V^(n=1)) to the trap-filled limit(I∝V^(n>3)) or the Child region (I∝V^(n=2)) (20,30,31). Here, forTOA-perovskites a remarkably low trap density n_(t(TOA))=(3.7±0.6)×10¹⁴cm⁻³ was determined, which is more than 10-fold lower than that ofSE-perovskite (n_(t(SE))=(7.8±0.5)×10¹⁵ cm⁻³). The elemental analysisthrough energy-dispersive X-ray spectroscopy indicates that remaining Clwas negligible (see FIG. 18). It is worth noting that the fp-TRMCexperiments measured the intrinsic characteristics of perovskite thinfilms in a dimension of 2.29×1.09 cm², rather than locally favoredcharacteristics; thus, the Cl presence, if there was any, was notcritical to the observed enhanced mobilities for TOA-perovskites.

The transient decay of ΦΣμ(t) signals and corresponding parameters withbi-exponential fitting results under I₀=˜7-8×10⁹ photons cm⁻² pulse⁻¹are shown in FIG. 15 Panel B and Table 1, respectively.

TABLE 1 Fitting results of either bi- (for TOA-perovskite) and single-(for SE-perovskite) exponential decay function for TRMC transients shownin FIG. 15 Panel B.^(a)) a₁ τ₁ a₂ τ₂ τ_(avg) (f₁) [ns] (f₂) [ns] [ns]TOA-perovskite 13.2 (0.02) 183 38.5 (0.98) 2840 2783 SE-perovskite 20.7(1.0)  1021 1021 ^(a))a_(i) is the prefactor of exponential decayfunction in ΦΣμ(t) = Σ_(i)a_(i) exp(−t/τ_(i)), and fi is the fractionalcontribution of each time constant (τ_(i))

The average lifetime τ_(avg) for TOA-perovskites was determined to be2.8 μs from τ_(avg) Uif τ_(i), where f_(i) is the fractionalcontribution of each time constant, whereas SE-perovskites exhibitedsingle-exponential decay with a 1.0-μs time constant. Although noattempt is made in this work to address the distinguished relaxationbehavior between TOA- and SE-perovskites, it is noteworthy that thesignificantly longer carrier lifetime in TOA-perovskites is consistentwith their improved material properties (e.g., enhanced crystallinity,low defect density, and compact coverage), allowing for a much longertime window to extract charges compared with SE-perovskite.

Planar organic-inorganic perovskite solar cells with 450-nm-thickinorganic-organic perovskite layers were fabricated to examine theeffect of TOA growth on photovoltaic (PV) properties. Referring to FIG.19, a first device 300A is shown on the right manufactured by the TOAmethods described herein, and a second device 300B made by conventionalsolvent engineering (SE) methods. These side-by-side images compare thefirst charge-transport layers (320A and 320B), the organic-inorganicperovskite layers (330A and 330B), the second charge-transport layers(340A and 340B), and additional layers (350A and 350B) for the twodevices (300A and 300B) respectively, where in this example theadditional layers (350A and 350B) are a contact layer The currentdensity-voltage (J-V) curves with various scan rate (or delay time),external quantum efficiency (EQE) spectra, and stabilized PCEs for TOA-and SE-PSCs are compared to understand the correlation between enhancedelectrical properties and device characteristics.

FIG. 20A shows the J-V curves for the champion device with both forwardand reverse scans and 50-ms delay time under AM 1.5G illumination. Forthe reverse scan, TOA-PSC shows a PCE of 19.7% with short-circuitcurrent voltage (J_(sc)) of 23.2 mA cm⁻², open-circuit voltage (V_(oc))of 1.08 V, and fill factor (FF) of 0.78, whereas SE-PSC delivers a lowerPCE of 15.7% with J_(sc) of 22.9 mA cm⁻², V_(oc) of 1.00 V, and FF of0.68. Hysteresis for TOA-PSC was also significantly reduced incomparison to SE-PSC. The PCE of TOA-PSC is 17.4% with forward-scan,corresponding to 88% of its reverse-scan PCE. In contrast, theforward-scan PCE (9.5%) of SE-PSC is only about 61% of its reverse-scanPCE. The improved device characteristics with TOA-PSCs are furtherconfirmed by the statistic PV parameters (see Tables 2 and 3 below) andefficiency distribution (see FIG. 21). The EQE spectra and theintegrated J_(sc) determined by EQE for TOA- and SE-PSCs are shown inFIG. 20B. The differences between J_(sc) and EQE-integrated J_(sc) are7.9% for SE-PSC (22.9 and 21.1 mA cm⁻², respectively) and only 2.2% forTOA-PSC (23.2 and 22.7 mA cm⁻², respectively). Although the difference(<10%) is reasonable for both devices, TOA-PSC showed more consistentresults between the J_(sc) and EQE measurement. These consistentimprovements in PV properties (including higher V_(oc) and FF, lesshysteresis, and negligible discrepancy between J_(sc) and EQE) ofTOA-PSCs can be ascribed to the enhanced charge-carrier mobility andlifetime of TOA-perovskite with (−111) uniaxial-orientation, much highercrystallinity, and lower defect/trap density. FIG. 20C compares thestable output of TOA- and SE-PSCs. TOA-PSC exhibited a stabilized PCE of19.0%, representing 96.4% of its reverse-scan PCE.

In contrast, SE-PSC showed a stabilized PCE of 13.4%, corresponding to85.3% of its reverse-scan PCE. A typical TOA-PSC (17.8% reverse-scanPCE) was analyzed and the cell performance was verified by using anasymptotic stabilization method, confirming a stabilized PCE of 17.2%(see FIG. 22B). This certified PCE corresponds to 96.5% of thereverse-scan PCE, which shows almost the same difference as shown inFIG. 20C. The hysteresis behavior of TOA- and SE-PSCs is furtherexamined by checking their forward- and reverse-scan PCEs as a functionof scan delay time from 0.01 to 3 s (see FIG. 20D). The PCEs werenormalized with respect to that measured with 50-ms delay under reversescan. For the SE-PSC, as the delay time was increased, the average PCEand hysteresis decreased. Interestingly, for TOA-PSC, the reverse-scanPCE did not depend on the scan delay time, whereas the forward-scan PCEincreased and approached the reversed-scan PCE with longer scan delay.With a 3-second scan delay, the average PCE reached about 96% ofreverse-scan PCE. Although more detailed investigations are necessary tounderstand the hysteresis behavior of TOA-PSCs, the negligiblediscrepancy between reverse-scan and stabilized PCEs, as well as theabsence of the scan-rate dependence of reverse-scan PCEs, likely resultfrom the unique structural and electro-optical properties of theTOA-perovskites discussed above.

TABLE 2 Photovoltaic parameters measured with 50-ms delay times inforward and reverse direction for 22 TOA-PSCs with a 0.12-cm² blackmetal aperture under AM 1.5 G illumination condition calibrated using astandard Si solar cell for every measurement. J_(sc) (mA cm⁻²) V_(oc)(V) FF PCE (%) Forward Reverse Forward Reverse Forward Reverse ForwardReverse #1 22.2 22.1 1.08 1.10 0.67 0.79 16.1 19.1 #2 22.2 22.2 0.961.00 0.64 0.77 13.8 17.0 #3 21.7 21.6 1.06 1.08 0.62 0.73 14.3 17.0 #422.2 22.2 0.98 1.04 0.63 0.76 13.7 17.6 #5 22.7 22.7 0.98 1.04 0.64 0.7214.3 17.1 #6 22.8 22.8 0.98 1.06 0.66 0.76 14.8 18.4 #7 22.6 22.5 1.041.08 0.61 0.75 14.3 18.1 #8 22.5 22.5 1.04 1.08 0.63 0.74 14.7 17.9 #922.6 22.4 1.08 1.10 0.63 0.74 15.3 18.2 #10 22.9 22.8 1.02 1.06 0.610.72 14.2 17.4 #11 23.3 23.2 1.06 1.09 0.71 0.78 17.4 19.7 #12 21.9 21.91.06 1.08 0.65 0.77 15.0 18.1 #13 23.3 23.2 1.04 1.08 0.65 0.77 15.719.4 #14 22.6 22.6 1.02 1.06 0.70 0.78 16.1 18.8 #15 22.7 22.7 1.02 1.080.67 0.77 15.6 18.8 #16 22.2 22.1 1.04 1.08 0.59 0.71 13.5 16.8 #17 22.522.5 1.00 1.06 0.70 0.78 15.8 18.5 #18 22.7 22.8 1.00 1.06 0.63 0.7414.3 17.9 #19 22.4 22.3 1.02 1.05 0.67 0.76 15.3 17.9 #20 22.6 22.5 1.021.06 0.67 0.75 15.3 17.9 #21 22.7 22.7 0.96 1.04 0.66 0.76 14.3 17.9 #2222.8 22.8 1.00 1.06 0.67 0.75 15.2 18.1 Average 22.6 ± 0.4 22.5 ± 0.41.02 ± 0.04 1.07 ± 0.02 0.65 ± 0.03 0.75 ± 0.02 15.0 ± 0.9 18.1 ± 0.8

TABLE 3 Photovoltaic parameters measured with 50-ms delay times inforward and reverse direction for 23 SE-PSCs under same measurementconditions applied to measurement of TOA-PSCs. J_(sc) (mA cm⁻²) V_(oc)(V) FF PCE (%) Forward Reverse Forward Reverse Forward Reverse ForwardReverse #1 22.0 21.9 0.98 1.04 0.33 0.69 7.2 15.8 #2 21.8 21.7 0.96 1.020.38 0.70 7.9 15.4 #3 22.4 22.4 0.94 1.00 0.41 0.67 8.5 15.0 #4 22.422.5 0.88 0.96 0.42 0.66 8.3 14.3 #5 22.6 22.6 0.92 1.02 0.34 0.66 7.115.2 #6 23.0 22.9 0.92 1.01 0.45 0.68 9.5 15.7 #7 22.4 22.4 0.94 1.020.41 0.65 8.6 14.8 #8 22.2 22.1 0.94 1.02 0.37 0.63 7.6 14.2 #9 22.522.5 0.92 1.00 0.44 0.69 9.1 15.5 #10 22.3 22.2 0.88 0.96 0.44 0.67 8.614.3 #11 22.3 22.2 0.90 1.00 0.45 0.64 9.0 14.2 #12 22.5 22.4 0.94 1.020.45 0.64 9.5 14.5 #13 22.8 22.8 0.88 0.98 0.47 0.66 9.4 14.8 #14 22.422.4 0.96 1.04 0.48 0.68 10.3 15.8 #15 22.7 22.8 0.90 0.98 0.38 0.65 7.714.5 #16 22.1 22.0 0.90 0.98 0.43 0.63 8.7 13.6 #17 22.7 22.8 0.88 0.980.47 0.68 9.5 15.2 #18 22.5 22.5 0.86 0.96 0.45 0.67 8.6 14.6 #19 21.821.7 0.94 1.02 0.36 0.64 7.4 14.2 #20 21.9 21.9 0.94 1.02 0.42 0.67 8.715.0 #21 22.2 22.1 0.94 1.04 0.42 0.66 8.8 15.1 #22 22.0 21.9 0.98 1.040.42 0.66 9.1 14.9 #23 22.3 22.2 0.92 1.02 0.41 0.67 8.4 15.2 Average22.3 ± 0.3 22.3 ± 0.4 0.92 ± 0.03 1.01 ± 0.03 0.42 ± 0.04 0.66 ± 0.028.6 ± 0.8 14.9 ± 0.6

Finally, the versatility of the TOA growth process described herein hasbeen demonstrated by applying it to other organic-inorganic perovskitecompositions including triple-cation and mixed-halide perovskites (e.g.,MAPbI_((3-y))Cl_(y), FA_(0.5)MA_(0.2)PbI_((3-y))Cl_(y), andFA_(0.55)MA_(0.4)Cs_(0.05)PbI_((2.9-y))Br_(0.1)Cl_(y)). All of theseorganic-inorganic perovskite thin films were grown by embodiments of theTOA processes described herein and demonstrated high-crystallineuniaxial orientation and uniform morphology with 2-5-μm grain sizes (seeFIGS. 23A and 23B). Thus, the TOA growth is promising as a generalsynthetic route for preparing perovskite thin films, featuring a highdegree of orientation and crystallinity, uniform and compact filmmorphology with several-micrometer grain sizes, high carrier mobilityand lifetime, and low defect density-all of which are preferred materialattributes for developing high-performance organic-inorganic perovskitesolar cells.

Materials and Methods

Preparation of organic-inorganic perovskite precursor solutions: Aprecursor solution for TOA-processed organic-inorganic perovskitecrystals and films having substantial orientation relative to a singlereference axis was prepared by dissolving a first FAI-PbI₂ reactant pairand a second 3MAI-PbCl₂ reactant pair at about a 3:2 ratio in anhydrousN,N-dimethylformamide (DMF) at 55° C. for about 4 hours. To form anorganic-inorganic perovskite film of oriented organic-inorganicperovskite crystals, having a thickness of about 450 nm, the precursorsolution was prepared using 0.95 M lead concentration. For thecrystallographic studies describe above, a precursor solution ofx(FAI-PbI₂)-(1-x)(3MAI-PbCl₂) (0≤x≤1), as described above, was dissolvedunder the same conditions. The 0.95 M (0.6FAI-0.4MAI-PbI₂) startingsolution, and the (0.6FAI-2.4MAI-PbCl₂) starting solution were alsoprepared under the same conditions, dissolved in DMF. For theconventional solvent-engineering process, the a 1.4 M precursor solutionwas prepared by dissolving HC(NH₂)₂I, CH₃NH₃I, and PbI₂ at a ratio of0.6:0.4:1 in a mixture of γ-butyrolactone (GBL) and dimethyl sulfoxide(DMSO) (7:3 v/v) at room temperature. Preparation of precursor wascarried out in a N₂-filled glovebox.

Solar cell fabrication: A patterned fluorine-doped tin oxide (FTO) wasdeposited with a compact TiO₂ blocking layer by spray pyrolysis at 450°C. using 0.2 M titanium diisopropoxide bis(acetylacetonate) in 1-butanolsolution, followed by 450° C. annealing for about 1 hour.Organic-inorganic perovskite starting solutions were deposited in a drynitrogen box using a spin coater to form a liquid coating of theorganic-inorganic perovskite starting solutions on the c-TiO₂/FTOsubstrate. Spin coating utilized a two-step procedure with a first stepof 500 rpm for about 15 seconds, and a second step of 2000 rpm for about45 seconds with sufficient dispensing of precursor solution on a1-inch-square c-TiO₂/FTO substrate.

For the control sample (randomly oriented perovskite using conventionalsolvent-engineering), the precursor solution was deposited on thesubstrate by spin-coating at 1,000 and 4,000 rpm for 60 seconds and 40seconds, respectively. At 30 seconds into spin-coating at 4,000 rpm, 0.7mL of diethyl ether was drop-casted on the spinning substrate.

After spin-coating both the TOA-processed sample and the control sample,the solid-state precursor (SSP) films were annealed (thermally treated)at about 50° C. for about 5 minutes, followed sequentially, by furtherannealing at about 130° C. for about 10 minutes. After annealing, 60 μLof a hole-transport layer (HTL) solution (72 mg of spiro-OMeTAD, 29 μLof 4-tert-butylpyridine, 17 μL of Li-TFSI solution (720 mg of Li-TFSI in1 mL acetonitrile) and 20 μL of FK102 Co(III) TFSI salt (300 mg FK102Co(III) TFSI in 1 mL acetonitrile) in 1 mL of chlorobenzene) wasspin-coated on the perovskite/c-TiO₂/FTO at 3,500 rpm for 30 seconds.Finally, a 130-nm Ag layer was deposited on the HTL by thermalevaporation with 0.15 nm s⁻¹ deposition rate. Before depositing of theorganic-inorganic perovskite layers and the HTL layers, all preparedsolutions were infiltrated through 0.45-μL-size PTEF filter.

Material characterization: The crystal structures of the preparedorganic-inorganic perovskite films were characterized using an X-raydiffractometer (XRD, D-Max 2200, Rigaku). Two-dimensional XRD (2D-XRD)was measured using a D8-Discover (Bruker) with GADDS 4-circle detector(General Area Detector Diffraction System). The morphologies andmicrostructures of the prepared perovskite films and the cross-sectionalstructure and thickness of the solar cells were investigated using afield-emission scanning electron microscopy (FESEM, Quanta 600 and Nova630 NanoSEM, FEI). Energy-dispersive X-ray spectroscopy (EDS) spectra ofperovskite were also obtained using the same scanning electronmicroscopy (Quanta 600) microscope. To analyze the cross-sectionalcrystal structure of single-oriented perovskite, perovskite films weretreated by focused ion beam (FIB, SMI3050SE, SII Nanotechnology), thenthe prepared sample was investigated using Cs-corrected transmissionelectron microscopy (Cs-TEM, JEM-ARM200F, JEOL). The optical absorptionspectra of perovskite films were measured using a UV-Visspectrophotometer with the aid of an integrated sphere (Cary-6000i,Agilent). The current-voltage measurements of perovskite films forspace-charge-limited current (SCLC) analysis were carried out with apotentiostat (Princeton Applied Research, VersaSTAT MC) under dark. Todeterminate permittivity of perovskite films, impedance spectroscopy wascarried out from 10⁴ to 10⁶ Hz, under dark, using a potentiostat(Princeton Applied Research, Parstat 2273).

Device characterization: Photovoltaic performance measurements weretaken under a simulated AM 1.5G illumination (100 mW cm⁻², Oriel Sol3AClass AAA Solar Simulator, Newport). The AM 1.5G sunlight was calibratedusing a standard Si solar cell (Oriel, VLSI standards) for everymeasurement. The photocurrent density-voltage (J-V) characteristics weremeasured using a Keithley 2400 source meter with 0.12-cm² black metalaperture. The stabilized current and power output were measured using apotentiostat (Princeton Applied Research, VersaSTAT MC). Externalquantum efficiency (EQE) spectra of devices were measured using a solarcell quantum-efficiency measurement system (QEX10, PV Measurements).

Flash-Photolysis Time-Resolved Microwave Conductivity (fp-TRMC): Thedetails of the fp-TRMC experimental setup, its theoretical background,and data analysis have been extensively reported elsewhere. In brief,our fp-TRMC uses a visible-pump/microwave-probe configuration, and asample is optically excited by a 4-ns full-width-at-half-maximum laserpulse from an optical parametric oscillator (OPO, Continuum Panther),pumped by the 355-nm harmonic of an Nd:YAG laser (Continuum Powerlite)and sample photoconductance (ΔG(t)) is measured by monitoring atransient change (ΔP(t)) in microwave power absorption by a sample aftera laser pulse as a function of delay time. A sample is mounted andsealed into a microwave cavity in a nitrogen glovebox, and transferredto the experimental apparatus where ultra-high-purity (UHP)-gradenitrogen flow through the cavity is maintained at all times to avoid anyambient exposure to humidity that can readily degrade organic/inorganicperovskites during experiments. Excitation pulse energy is adjusted witha series of neutral-density filters and measured by a laser-energy meter(Coherent, EPM2000 power meter, J25 and J-10SI-HE energy sensors). Wemeasured the electronic absorption spectrum of a sample before and afterfp-TRMC experiments to ensure that a sample is robust. Theperovskite/quartz samples are prepared through the same procedurementioned in the solar cell fabrication section.

Below, Equation 1 shows the relations between experimentally obtainedtransient microwave power difference (ΔP(t)) to photoconductance (ΔG(t))and the product (ΦΣμ(t)) of carrier-generation yield (Φ(t)) and the sum(Σμ=μ_(e)+μ_(h)) of electron and hole mobilities:

$\begin{matrix}{{{- \frac{\Delta {P(t)}}{P}} = {{K\Delta {G(t)}} = {K\beta {q_{e}\left( {{\Phi (t)}{\Sigma\mu}} \right)}\left( {I_{0}F_{A}} \right)}}},} & (1)\end{matrix}$

where K [Ω] is a sensitivity factor, determined as 28,200 from thecavity resonance characteristics and the dielectric properties of themedium, β is the ratio between the long and short axes of the samplevolume, q_(e) [C] is the elementary charge, I₀ [photons cm⁻² pulse⁻¹] isthe excitation photon fluence, and F_(A) is the fraction of lightabsorbed at the excitation wavelength (absorptance).

Calculation of degree of {−111} crystallographic orientation(DCO_({−111})): The relative degree of {−111} crystallographicorientation was calculated from Equation 2 as below:

$\begin{matrix}{\frac{\Sigma {\int I_{\{{{- 1}11}\}}}}{\Sigma {\int I_{({{other}\mspace{14mu} {hkl}})}}},} & (2)\end{matrix}$

where N is the number of diffractions considered in the analysis; and∫I_((hkl)) is integrated 2D-XRD spectra of each plane, corresponding to(−111), (−120), (021), (−222), (−231), and (−240) planes. ForMAPbI_((3-x))Cl_(x) perovskite (at x=0), the (110), (112), (211), (220),(310), and (024) planes were selected.

Evaluation of real-part contribution for photoconductivity to TRMCtransient signals: fp-TRMC experiments probe the time-dependent complexdielectric constant ε of the sample after photoexcitation, which isrevealed as microwave power difference (ΔP). Conductivity has a relationto dielectric constant as σ=iωε=ε₀ω(iε′+ε″), where σ, ω, ε₀, ε′, and ε″represent the complex conductivity, radian frequency of the microwaveelectric field, vacuum permittivity, and real and imaginary parts of thedielectric constant at frequency co, respectively. This leads to thereal photoconductivity being proportional to the imaginary dielectricconstant change, which appears as microwave absorption. The imaginaryphotoconductivity is proportional to the change in the real dielectricconstant, revealing a shift in the microwave-cavity resonance frequency.In this regard, the contour plots of frequency-dependent reflectedmicrowave power transients shown in FIG. 18 Panel A can evaluate theorigin of photoconductance; for samples in this work, the imaginary-partcontributions of photoconductivity are negligible.

Determination of trap density of TOA- and SE-perovskite film: The trapdensity, n_(t), of perovskite films are determined from the onsetvoltage, called trap-filled limited voltage (V_(TFL)), of I-V curvesusing Equation 3 as below:

$\begin{matrix}{{V_{TFL} = \frac{en_{t}d^{2}}{2ɛɛ_{0}}},} & (3)\end{matrix}$

where e is elementary charge, n_(t) is trap density, d is the thicknessof perovskite films (d_((TOA))=1.2 μm and d_((SE))=550 nm,respectively), ε₀ is vacuum permittivity, and ε is relative dielectricconstant of perovskite. In this study, ε of perovskite films wasdetermined from impedance spectroscopy using Equation 4 as below:

$\begin{matrix}{{{ɛ(f)} = {\frac{d}{Aɛ_{0}}\frac{- 1}{2\pi \; f\; {{Im}(Z)}}}},} & (4)\end{matrix}$

where d is the thickness of perovskite film between two parallelelectrodes, A is the capacitor area, and ε₀ is vacuum permittivity.Consequently, we determined relative dielectric constant ε=60 of ourmixed-cation perovskite films.

EXAMPLES Example 1

A method comprising: combining a first organic salt (A¹X¹), a firstmetal salt (M¹(X²)₂), a second organic salt (A²X³), a second metal salt(M²Cl₂), and a solvent to form a primary solution, wherein: A¹X¹ andM¹(X²)₂ are present in the primary solution at a first ratio betweenabout 0.5 to 1.0 and about 1.5 to 1.0; and A²X³ to M²Cl₂ are present inthe primary solution at a second ratio between about 2.0 to 1.0 andabout 4.0 to 1.0.

Example 2

The method of Example 1, wherein A¹ comprises at least one of an alkylammonium, an alkyl diamine, cesium, or rubidium.

Example 3

The method of Example 2, wherein A¹ comprises at least one ofmethylammonium, ethylammonium, propylammonium, or butylammonium.

Example 4

The method of Example 3, wherein A¹ is methylammonium.

Example 5

The method of Example 2, wherein A¹ is formamidinium.

Example 6

The method of Example 1, wherein A² comprises at least one of an alkylammonium, an alkyl diamine, cesium, or rubidium.

Example 7

The method of Example 6, wherein A² comprises at least one ofmethylammonium, ethylammonium, propylammonium, or butylammonium.

Example 8

The method of Example 7, wherein A² is methylammonium.

Example 9

The method of Example 6, wherein A² is formamidinium.

Example 10

The method of Example 6, wherein: A² comprises an alkyl ammonium andcesium, and the alkyl ammonium is methylammonium.

Example 11

The method of Example 1, wherein at least one of A¹ or A² comprises atleast one of an alkyl ammonium, an alkyl diamine, cesium, or rubidium.

Example 12

The method of Example 11, wherein at least one of A¹ or A² comprises atleast one of methylammonium, ethylammonium, propylammonium, orbutylammonium.

Example 13

The method of Example 11, wherein at least one of A¹ or A² comprisesformamidinium.

Example 14

The method of Example 11, wherein A¹ comprises methylammonium and A²comprises formamidinium.

Example 15

The method of Example 11, wherein A¹ comprises methylammonium and A²comprises formamidinium and cesium.

Example 16

The method of Example 1, wherein M¹ comprises a metal having a 2+valence state.

Example 17

The method of Example 16, wherein M¹ comprises at least one of lead,tin, or germanium.

Example 18

The method of Example 17, wherein M¹ is lead.

Example 19

The method of Example 1, wherein M² comprises a metal having a 2+valence state.

Example 20

The method of Example 19, wherein M² comprises at least one of lead,tin, or germanium.

Example 21

The method of Example 20, wherein M² is lead.

Example 22

The method of Example 1, wherein at least one of M¹ or M² comprises ametal having a 2+ valence state.

Example 23

The method of Example 22, wherein at least one of M¹ or M² comprises atleast one of lead, tin, or germanium.

Example 24

The method of Example 1, wherein X¹ comprises a halogen.

Example 25

The method of Example 24, wherein X¹ comprises at least one of fluorine,bromine, iodine, or astatine.

Example 26

The method of Example 25, wherein X¹ comprises at least one of bromineor iodine.

Example 27

The method of Example 1, wherein X² comprises a halogen.

Example 28

The method of Example 27, wherein X² comprises at least one of fluorine,bromine, iodine, or astatine.

Example 29

The method of Example 28, wherein X² comprises at least one of bromineor iodine.

Example 30

The method of Example 1, wherein X³ comprises a halogen.

Example 31

The method of Example 30, wherein X³ comprises at least one of fluorine,bromine, iodine, or astatine.

Example 32

The method of Example 31, wherein X³ comprises at least one of bromineor iodine.

Example 33

The method of Example 1, wherein at least one of X¹, X², or X³ comprisesa halogen.

Example 34

The method of Example 33, wherein at least one of X¹, X², or X³comprises at least one of fluorine, bromine, iodine, or astatine.

Example 35

The method of Example 34, wherein X¹ is iodine and X² is bromine.

Example 36

The method of Example 1, wherein the solvent comprises an organicsolvent.

Example 37

The method of Example 36, wherein the solvent comprises at least one ofγ-butyrolactone or dimethyl sulfoxide.

Example 38

The method of Example 37, wherein the solvent comprises at least one ofdimethylformamide, dimethylacetamide, γ-butyrolactone, dimethylsulfoxide, or N-methyl-2-pyrrolidone.

Example 39

The method of Example 1, wherein the first ratio is about 1.0. to 1.0.

Example 40

The method of Example 1, wherein the second ratio is about 3.0 to 1.0.

Example 41

The method of Example 1, wherein: A¹X¹ and M¹(X²)₂ form a first reactantpair, A²X³ to M²Cl₂ form a second reactant pair, and the first reactantpair and the second reactant pair are present in the primary solution ata third ratio between about 1.0 to 1.0 and about 1.5 to 1.

Example 42

The method of Example 1, wherein at least one of A¹X¹, M¹(X²)₂, A²X³, orM²Cl₂ is present in the primary solution at a molar concentrationbetween about 0.1 M and about 2.0 M.

Example 43

The method of Example 1, wherein the combining is performed at a firsttemperature between about 25° C. and about 80° C.

Example 44

The method of Example 1, wherein the combining is performed for a firstperiod between about 0.5 hours and about 12 hours.

Example 45

The method of Example 1, wherein the combining comprises: a firstcombining of the first organic salt (A¹X¹) and the first metal salt(M¹(X²)₂) in a first solvent to form a first solution containing thefirst ratio; a second combining of the second organic salt (A²X³) andthe second metal salt (M²Cl₂) in a second solvent to form a secondsolution containing the second ratio; and a third combining of the firstsolution with the second solution to form the primary solution.

Example 46

The method of Example 45, wherein the first solvent and the secondsolvent are the same.

Example 47

The method of Example 45, wherein the first solvent comprises an organicsolvent.

Example 48

The method of Example 47, wherein the first solvent comprises at leastone of γ-butyrolactone or dimethyl sulfoxide.

Example 49

The method of Example 48, wherein the first solvent comprises at leastone of dimethylformamide, dimethylacetamide, γ-butyrolactone, dimethylsulfoxide, or N-methyl-2-pyrrolidone.

Example 50

The method of Example 45, wherein the second solvent comprises anorganic solvent.

Example 51

The method of Example 50, wherein the second solvent comprises at leastone of γ-butyrolactone or dimethyl sulfoxide.

Example 52

The method of Example 51, wherein the second solvent comprises at leastone of dimethylformamide, dimethylacetamide, γ-butyrolactone, dimethylsulfoxide, or N-methyl-2-pyrrolidone.

Example 53

The method of Example 1, further comprising: depositing at least aportion of the primary solution onto a solid surface, wherein: thedepositing forms a liquid layer comprising the primary solution on thesolid surface.

Example 54

The method of Example 53, wherein the depositing is performed using atleast one of spin coating, blade coating, curtain coating, or dipcoating.

Example 55

The method of Example 53, wherein the liquid layer has a thicknessbetween about 100 nm and about 3000 nm.

Example 56

The method of Example 53, further comprising, after the depositing:treating at least the liquid layer, wherein: the treating converts atleast a portion of the liquid layer to a solid layer comprising aplurality of organic-inorganic perovskite crystals, and the solid layeris adhered to the solid surface.

Example 57

The method of Example 56, wherein the treating is performed by thermaltreating.

Example 58

The method of Example 57, wherein the thermal treating is performed byheating at least the liquid layer to a second temperature greater thanabout 120° C.

Example 59

The method of Example 58, wherein the second temperature is betweengreater than about 120° C. and about 200° C.

Example 60

The method of Example 56, wherein the plurality of organic-inorganicperovskite crystals comprise A¹ _((1-x-y))A² _(x)A^(3y)M¹ _(z)M²_(1-z)X¹ _(a)X² _(b)X³ _(c)Cl_(d), where x, y, and z are each betweenzero and one inclusively, and a+b+c+d=3.0.

Example 61

The method of Example 60, wherein the plurality of organic-inorganicperovskite crystals comprise FA_(0.6)MA_(0.4)PbI_((3-d))Cl_(d).

Example 62

The method of Example 60, wherein the plurality of organic-inorganicperovskite crystals comprise MAPbI_((3-d))Cl_(d).

Example 63

The method of Example 60, wherein the plurality of organic-inorganicperovskite crystals comprise FA_(0.5)MA_(0.2)PbI_((3-d))Cl_(d).

Example 64

The method of Example 60, wherein the plurality of organic-inorganicperovskite crystals compriseFA_(0.55)MA_(0.4)Cs_(0.05)PbI_((2.9-d))Br_(0.1)Cl_(d).

Example 65

The method of Example 56, wherein: each of the plurality oforganic-inorganic perovskite crystals has a length dimension and a widthdimension, and the length dimension and the width dimension define anaspect ratio of the length dimension to the width dimension betweenabout 1.5 and about 50.

Example 66

The method of Example 65, wherein the length dimension is orientedsubstantially perpendicular to the solid surface.

Example 67

The method of Example 65, wherein the length dimension is between about100 nm and about 3000 nm.

Example 68

The method of Example 56, wherein the plurality of organic-inorganicperovskite crystals form grains measuring between about 2 μm and about 5μm.

Example 69

The method of Example 53, wherein a first charge transport layercomprises the solid surface.

Example 70

The method of Example 69, wherein the first charge transport layercomprises at least one of TiO₂, SnO₂, ZnO, spiro-OMeTAD,poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), orpoly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS).

Example 71

A device comprising: a perovskite layer comprising an organic-inorganicperovskite crystal, wherein: the perovskite layer is positionedsubstantially parallel with a plane, the organic-inorganic perovskitecrystal has a molar composition defined by A¹ _((1-x-y))A² _(x)A^(3y)M¹_(z)M² _(1-z)Cl_(d), where x, y, and z are each between zero and oneinclusively, and d=3.0, at least one of A¹, A², or A³ comprises at leastone of an alkyl ammonium, an alkyl diamine, cesium, or rubidium, and atleast one of M¹ or M² comprises a metal having a 2+ valence state.

Example 72

The device of Example 71, wherein the alky ammonium comprises at leastone of methylammonium, ethylammonium, propylammonium, or butylammonium.

Example 73

The device of Example 71, wherein the alky ammonium comprises ismethylammonium.

Example 74

The device of Example 71, wherein the alkyl diamine comprisesformamidinium.

Example 75

The device of Example 71, wherein A¹ comprises methylammonium and A²comprises formamidinium.

Example 76

The device of Example 71, wherein A¹ comprises methylammonium, A²comprises formamidinium, and A³ comprises cesium.

Example 77

The device of Example 71, wherein the metal comprises at least one oflead, tin, or germanium.

Example 78

The device of Example 71, wherein M¹ comprises lead.

Example 79

The device of Example 71, wherein: the organic-inorganic perovskitecrystal further comprises X¹ _(a)X² _(b)X³ _(c), where a+b+c+d=3.0, andat least one of X¹, X², or X³ comprises a halogen.

Example 80

The device of Example 79, wherein the halogen comprises at least one offluorine, chlorine, bromine, iodine, or astatine.

Example 81

The device of Example 79, wherein X¹ comprises iodine.

Example 82

The device of Example 79, wherein the organic-inorganic perovskitecrystal comprises FA_(0.6)MA_(0.4)PbI_((3-d))Cl_(d).

Example 83

The device of Example 79, wherein the organic-inorganic perovskitecrystal comprises MAPbI_((3-d))Cl_(d).

Example 84

The device of Example 79, wherein the organic-inorganic perovskitecrystal comprises FA_(0.5)MA_(0.2)PbI_((3-d))Cl_(d).

Example 85

The device of Example 79, wherein the organic-inorganic perovskitecrystal comprises FA_(0.55)MA_(0.4)Cs_(0.05)PbI_((2.9-d))Br_(0.1)Cl_(d).

Example 86

The device of Example 79, wherein: the organic-inorganic perovskitecrystal has a length dimension and a width dimension, and the lengthdimension and the width dimension define an aspect ratio of the lengthdimension to the width dimension between about 1.5 and about 50.

Example 87

The device of Example 86, wherein the length dimension is orientedsubstantially perpendicular to the plane.

Example 88

The device of Example 86, wherein the length dimension is between about100 nm and about 3000 nm.

Example 89

The device of Example 71, wherein the organic-inorganic perovskitecrystal forms a grain having a width between about 2 μm and about 5 μm.

The foregoing discussion and examples have been presented for purposesof illustration and description. The foregoing is not intended to limitthe aspects, embodiments, or configurations to the form or formsdisclosed herein. In the foregoing Detailed Description for example,various features of the aspects, embodiments, or configurations aregrouped together in one or more embodiments, configurations, or aspectsfor the purpose of streamlining the disclosure. The features of theaspects, embodiments, or configurations, may be combined in alternateaspects, embodiments, or configurations other than those discussedabove. This method of disclosure is not to be interpreted as reflectingan intention that the aspects, embodiments, or configurations requiremore features than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment, configuration, oraspect. While certain aspects of conventional technology have beendiscussed to facilitate disclosure of some embodiments of the presentinvention, the Applicants in no way disclaim these technical aspects,and it is contemplated that the claimed invention may encompass one ormore of the conventional technical aspects discussed herein. Thus, thefollowing claims are hereby incorporated into this Detailed Description,with each claim standing on its own as a separate aspect, embodiment, orconfiguration.

1. A method comprising: combining a first organic salt (A¹X¹), a firstmetal salt (M¹(X²)₂), a second organic salt (A²X³), a second metal salt(M²Cl₂), and a solvent to form a primary solution, wherein: A¹X¹ andM¹(X²)₂ are present in the primary solution at a first ratio betweenabout 0.5 to 1.0 and about 1.5 to 1.0; and A²X³ to M²Cl₂ are present inthe primary solution at a second ratio between about 2.0 to 1.0 andabout 4.0 to 1.0.
 2. The method of claim 1, wherein at least one of A¹or A² comprises at least one of an alkyl ammonium, an alkyl diamine,cesium, or rubidium.
 3. The method of claim 2, wherein at least one ofA¹ or A² comprises at least one of methylammonium, ethylammonium,propylammonium, or butylammonium.
 4. The method of claim 2, wherein atleast one of A¹ or A² comprises formamidinium.
 5. The method of claim 1,wherein at least one of M¹ or M² comprises a metal having a 2+ valencestate.
 6. The method of claim 5, wherein at least one of M¹ or M²comprises at least one of lead, tin, or germanium.
 7. The method ofclaim 1, wherein at least one of X¹, X², or X³ comprises a halogen. 8.The method of claim 7, wherein at least one of X¹, X², or X³ comprisesat least one of fluorine, bromine, iodine, or astatine.
 9. The method ofclaim 1, wherein the solvent comprises an organic solvent.
 10. Themethod of claim 1, wherein: A¹X¹ and M¹(X²)₂ form a first reactant pair,A²X³ to M²Cl₂ form a second reactant pair, and the first reactant pairand the second reactant pair are present in the primary solution at athird ratio between about 1.0 to 1.0 and about 1.5 to
 1. 11. The methodof claim 1, further comprising: depositing at least a portion of theprimary solution onto a solid surface, wherein: the depositing forms aliquid layer comprising the primary solution on the solid surface. 12.The method of claim 11, wherein the depositing is performed using atleast one of spin coating, blade coating, curtain coating, or dipcoating.
 13. The method of claim 11, further comprising, after thedepositing: treating at least the liquid layer, wherein: the treatingconverts at least a portion of the liquid layer to a solid layercomprising a plurality of organic-inorganic perovskite crystals, and thesolid layer is adhered to the solid surface.
 14. The method of claim 13,wherein the plurality of organic-inorganic perovskite crystals compriseA¹ _((1-x-y))A² _(x)A³ _(y)M¹ _(z)M² _(1-z)X¹ _(a)X² _(b)X³ _(c)Cl_(d),where x, y, and z are each between zero and one inclusively, anda+b+c+d=3.0. 15-23. (canceled)